1. Field of the Invention
The present invention relates to plows, snow removal equipment and, more particularly, to devices for protecting plows and snow removal equipment against damage from impact with road obstructions.
2. Related Art
Modern snow removal devices, such as vehicle-mounted snow throwers and snowplows, typically are mounted to the front and rear ends of light, medium, and heavy-duty trucks, front end loaders, back hoes, tractors, graders, and similar vehicles. Snowplow blades typically include a curved moldboard which is mounted on a frame. Snow throwers and plows alike have a wear-strip, often made of steel, which may be mounted to the bottom of the frame to act as a scraping blade to remove snow from the ground and to direct the snow onto the moldboard. This action of both types of snow removal equipment will be referred to herein as “plowing.”
Roads and other plowing surfaces may include a variety of irregularities and obstructions, such as raised manhole covers, rocks, raised or cracked road sections and debris which has become frozen into the ground. Such obstacles may lie partially or completely beneath the surface of the snow and therefore be hidden from the plow operator's view. There is always a risk that the plow blade edge or other portion of the plow will strike such an obstruction while plowing. In addition to such unforeseen obstructions, known road features (such as curbs and berms) may be hidden from the plow operator by the snow. There is always a risk, therefore, that the plow operator will miscalculate the distance to such a known road feature and fail to stop the plow before it impacts the hidden road feature.
The plow blade may strike the obstruction with significant force, which is then transferred rearward from the plow blade to the plow assembly, the attached vehicle, and the vehicle operator. Such impacts may be significant not only at faster plowing speeds of 25–30 mph, but even at slower speeds of 10–15 mph. The force of such an impact may not only cause a sudden deceleration of the plow and attached vehicle, but may also cause the plow to violently and completely stop the vehicle. In some cases the plow may deflect off the obstruction and jump into the air. In some other cases the bolts holding the cutting edge have been known to shear, causing the cutting edge to flip through the air, thereby becoming a dangerous projectile and road hazard. This response to hitting an obstruction may not only cause significant damage to the plow and truck, but also cause personal injury to the plow operator and other nearby vehicles. Although driving at slower speeds may decrease the damage caused by such impacts, slower speeds decrease plowing efficiency. Furthermore, driving at slower speeds still does not completely eliminate impacts because, as described above, obstructions may be completely hidden from view and therefore be unavoidable even to the most careful of operators.
As a result of these problems, various efforts have been made to design plows to minimize the undesirable consequences just described. For example, many existing snow plow blades are equipped with a blade trip mechanism, also referred to as a “trip edge” or “trip assembly,” which allows the bottom of the plow blade to yield (“trip”) upon substantial impact. Conventional trip edges are described, for example, in U.S. Pat. No. 6,618,965, entitled “Cushion Stop and Method for Absorbing Bidirectional Impact of Snow Plow Blade Tripping.” In general, the plow blade is enabled to trip upon impact by mounting the snow plow blade on its support structure using a pivoting mechanism. The plow blade may, for example, be mounted on the support structure at a height of 8–16 inches above the ground. The pivoting mechanism enables the bottom of the snow plow blade to pivot in a rearward direction when the blade impacts an obstruction. The top of the snow plow blade pivots forward as the bottom of the snow plow blade pivots rearward in response to the force imposed by the obstruction. This rearward pivoting of the bottom of the snow plow blade in response to impacting an obstruction is referred to as “tripping.”
Typically, one or more strong springs (referred to as “trip springs”) are mounted behind the snow plow blade to resist tripping the blade edge except in response to a sufficiently strong rearward force. When the snow plow blade is in its normal (untripped) position, the trip springs are under tension, holding the blade edge in place. When the bottom of the snow plow blade is forced backward by an obstruction, the trip springs provide a resistive force which tends to absorb at least some of the force of impact with the obstruction. The force of such an impact may be reduced by this energy absorption, but still will impose some deceleration of the plow and attached vehicle. It may also cause the plow to violently lift into the air, sometimes by two feet or more, and then rapidly fall, impacting the ground. When the tripping force imposed by the obstruction is removed, the trip springs provide a restorative force which returns the snow plow blade to its normal (untripped) plowing position.
In the absence of trip springs, or if the biasing force provided by the trip springs is not sufficiently strong, the blade edge might trip too easily, such as upon contacting wet snow. As a result, trip springs typically are chosen to be quite strong. The restorative force, therefore, provided by the trip springs upon removal of the obstructive force also tends to be quite strong. The trip springs may, therefore, cause the snow plow blade to return to its normal plowing position with significant force, thereby causing a significant impact between the plow blade and its supporting structure. In the case where the plow is violently lifted into the air and the plow assembly drops to the plowing surface with all its weight, this impact may result in damage to the snow plow blade, its supporting structure, the plow's many components and/or to the vehicle. This represents one disadvantage of plow protection mechanisms which rely solely on trip edges.
Another problem faced by plow operators is that regions of the plow, such as the blade edge, that are in contact with the plowing surface are subject to significant wear due to friction and other forces, particularly when plowing is performed on asphalt or other hard road surfaces. In the case of the plow blade, such wear decreases plowing efficiency over time. In general, a plow cutting edge may typically be replaced one or two times each plowing season, and a set of wear pads may be replaced as frequently as once per snow storm. Both of these components may be replaced more frequently depending on the amount of plowing that is performed and plowing and road conditions. More generally, all components that are subject to wear require periodic replacement due to such wear. It is desirable, therefore, to take steps to reduce or minimize the impact of wear, and thereby to increase the useful life of components, thereby decreasing plow downtime and component replacement frequency, and in turn increasing plowing efficiency and decreasing the overall cost of maintenance.
One technique that has been employed to decrease wear is to provide wheels and/or wear guards which are attached to the moldboard, behind the plow blade edge, to support part of the load on the blade, thereby prolonging the time until the blade must be replaced. Even such protective devices, however, eventually wear out and are damaged, requiring replacement. Therefore, it is desirable to increase the life of protective devices such as wear guards, thereby decreasing the total cost of maintenance.